Optical recording medium

ABSTRACT

An optical recording medium includes a disc including a dye layer and a reflecting layer formed on a substrate, a dummy substrate, and an adhesive layer adhering the disc and the dummy substrate.

FIELD OF THE INVENTION

The present invention relates to an optical recording medium such as adigital versatile disk-recordable (DVD-R) or digital versatiledisc+recordable (DVD+R) disc.

DESCRIPTION OF RELATED ART

FIG. 1 is a cross-sectional view illustrating a conventional opticalrecording medium. A DVD-R/+R disc which is a “write once” format isdescribed as an example of the optical recording medium hereinafter.

The DVD-R/+R disc 100 of FIG. 1 includes a disc 110 and a dummy disc120. The disc 110 includes a dye layer 11, a reflecting layer 12 and apassivation layer 13 which are sequentially stacked on a poly carbonatesubstrate 10. The polycarbonate substrate 10 includes pregrooves (notshown) to guide a laser light during a recording operation and areproducing operation and has a thickness of 0.6 mm. The dummy disc 120includes a reflecting layer 16, a dye layer 17 and a passivation layer18 which sequentially are stacked on a dummy substrate 15. At thispoint, the reflecting layer 16 or/and the dye layer 17 of the dummy disc120 is/are optionally formed. The disc 110 and the dummy disc 120 areattached to each other through an adhesive layer 14.

The dye layers 11 and 17 are formed by coating an organic dye on thesubstrates 10 and 15, respectively, and serve as a recording layer thatinduces a decomposition or a transformation of a dye and atransformation of the substrates because they absorb a recording lightto emit light.

The reflecting layers 12 and 16 reflect a recording light and areproducing light to provide such an amount of light that a lightdetector can detect a modulation degree of a recording signal.

The passivation layers 13 and 18 prevent the reflecting layers 12 and 16from be transformed during a recording operation, and also separates thereflecting layers 12 and 16 from the adhesive layer 14 to prevent thedye layers or the reflecting layers from be chemically damaged.

The adhesive layer 14 has an adhesive strength enough to firmly attachthe two discs 110 and 120. A method for attaching the two discs 110 and120 includes a high melting technique, a screen printing technique usinga cationic UV adhesive, and a spin coating technique using a freeradical UV adhesive.

When the two discs 110 and 120 are adhered through the adhesive layer14, the following several parameters such as a moisture resistance, aheat resistance, an impact resistance, and the like should beconsidered.

A small amount of a monomer that is not reacted after a curing candamage the passivation layer and the reflecting layer. This can resultin recording characteristics deterioration of the DVD-R/+R disc. Such arecording characteristics deterioration is accelerated by a moisture anda heat. Various methods are employed in order to protect the reflectinglayer from a moisture and a heat. For example, the reflecting layer ismade with a special material, or the organic dye layer is made of astable dye.

Also, a sufficient adhesive strength should be secured for the DVD-R/+Rdisc 100 to endure a physical shock or impact.

Japanese laid-open publicationno. hei 10-27383 discloses an opticalinformation medium. In order to improve an impact resistance and amoisture resistance, the optical information medium is provided with thedisk forming a light interference layer and a reflection layer in atleast one side surface of a planer translucent substrate and anotherplaner disk stuck to the surface formed with the light interferencelayer and the reflection layer of the disk, and is constituted so that asignal is recorded by forming a pit bringing interference of lightpartially different from other parts to incident light and reflect lightof reproducing laser light on the light interference layer by theirradiation of a recording laser light from the translucent substrateside. Margin parts without forming the light interference layer areprovided on an outer peripheral side and an inner peripheral side of asignal recording area recording a signal on the disk, and the surfacecontaining the margin parts of the side provided with the lightinterference layer of the disk is stuck with another disk.

Also, Japanese laid-open publication no. hei 10-106037 discloses anoptical information recording medium. In order to enhance joint forcewith a recording layer joined to this area by surface machining an areafrom an outside end part to a side surface of a substrate, the opticalinformation recording medium is a sandwich type constituted so that adisk like substrate provided with a recording layer, a reflection layerand a protection layer in this order and having a hole part on itscenter is stuck to a disk like protection plate with the same shape asthis substrate so that the recording layer side becomes the insiderespectively through an adhesive. Then, an area (a corner part that bothsurfaces are intersected) from the outside end part surface of thesubstrate having the recording layer to its side surface is chamfered,and the recording layer is joined to the area performed with thechamfering process. Further, the outside end part of the inside of thedisk like substrate is preferred to be chamfered.

However, the conventional optical recording mediums necessitate thepassivation layers. Since the passivation layers are cured by a UV lightafter coating a UV curable resin, a manufacturing process iscomplicated, and also the optical recording medium can be bent by a heatgenerated during a curing of the UV curable resin.

SUMMARY OF THE INVENTION

To overcome the problems described above, preferred embodiments of thepresent invention provide an optical recording medium having a highimpact resistance or high durability without any passivation layers.

It is another object of the present invention to provide an opticalrecording medium having a simplified manufacturing process.

It is a still another object of the present invention to provide anoptical recording medium having excellent recording characteristics.

In order to achieve the above object, the preferred embodiments of thepresent invention provide an optical recording medium. The opticalrecording medium includes a disc including a dye layer and a reflectinglayer formed on a substrate, and a dummy substrate. The disc and thedummy substrate are adhered to each other through an adhesive layer.

An adhesive of the adhesive layer is cured by UV-light. The adhesivelayer has a viscosity of 300 cps to 900 cps at 25° C., a glasstransition temperature Tg after a curing of more than 30° C., a hardnessafter a curing of more than “H”, and an amount of the remaining monomerafter a curing of within 10%. The reflecting layer covers exposedportions of the dye layer, and the adhesive layer covers exposedportions of the reflecting layer. Adhesion enforcing regions arearranged on both an inner peripheral region and an outer peripheralregion of the optical recording medium.

The optical recording medium further includes a reflecting layer formedon the dummy substrate. The reflecting layer comprises Ag, Au, Al, Cu,or their alloy. The dye layer comprises a cyanine-based dye, ahemicyanine-based dye, an azo-based dye, a triphenylmetane-based dye, ora combination of two or more thereof. The adhesive layer has a thicknessof 10 μm to 80 μm.

The present invention has the following advantages. firstly, since thepassivation layer is not arranged, a manufacturing process issimplified, and also excellent recording characteristics, excellent heatresistance and excellent moisture resistance can be achieved. Further,due to an adhesion enforcing region formed on both an inner peripheralregion and an outer peripheral region of the disc, an adhesion strengthbetween the two substrates is improved, leading to a high durability.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which likereference numerals denote like parts, and in which:

FIG. 1 is a cross-sectional view illustrating a conventional opticalrecording medium;

FIG. 2 is a cross-sectional view illustrating an optical recordingmedium according to a preferred embodiment of the present invention;

FIG. 3 is a cross-sectional view illustrating an optical recordingmedium according to another preferred embodiment of the presentinvention

FIG. 4 is a cross-sectional view an optical recording medium of Example1 according to the preferred embodiments of the present invention; and

FIG. 5 is a cross-sectional view illustrating an optical recordingmedium of Comparison example 3.

DETAILED DESCRIPTION OF PREFFERED EMBODIMENTS

Reference will now be made in detail to preferred embodiments of thepresent invention, example of which is illustrated in the accompanyingdrawings.

FIG. 2 is a cross-sectional view illustrating an optical recordingmedium according to the preferred embodiment of the present invention. ADVD-R/+R disc is described hereinafter as one example of the opticalrecording medium according to the preferred embodiment of the presentinvention.

The DVD-R/+R disc 200 of FIG. 2 includes a disc 210 and a dummysubstrate 25, wherein the disc 210 includes a dye layer 21 and areflecting layer 22 formed on a substrate 20. The disc 210 and the dummysubstrate 25 are adhered to each other through an adhesive layer 23.

The substrate 20 includes pregrooves (not shown) to guide a laser lightduring a recording operation and a reproducing operation, and ismanufactured by an injection molding using a stamper. The substrate 20has a thickness of 0.5 mm to 0.6 mm and comprises one of polycarbonate,polymethyl methacrylate, epoxy resin, polyester, and amorphouspolyolefine.

The dye layer 21 is formed by dissolving an organic dye in an organicsolvent and then coating it on the substrate 20. The dye layer 21comprises a cyanine-based dye, a hemicyanine-based dye, an azo-baseddye, a triphenylmetane-based dye, or a combination of two or morethereof.

The reflecting layer 22 is formed by depositing a metal layer on thedried dye layer 21 using a sputtering technique. Preferably, thereflecting layer 22 has a thickness of 100 nm, and comprises Au, Ag, Al,Cu, or their alloy.

The disc 210 and the dummy substrate 25 are adhered by the followingmethod: first, an adhesive is applied on a portion of the reflectinglayer 22, and the dummy substrate 25 is laid on the reflecting layer 22on which the adhesive is coated. In this state, the disc 210 and thedummy substrate 25 is spin-coated at a high rotation speed. That is, theadhesive applied on a portion of the reflecting layer 22 is spread overthe entire surfaces of the reflecting layer 22 and the dummy substrate25 by a spin coating technique. Thereafter, a UV-light is radiated tocure the adhesive, whereupon the disc 210 and the dummy substrate 25 arefirmly adhered to each other. At this point, a thickness of the adhesivelayer 23 depends on a temperature, a viscosity of the adhesive, and arotation speed during a spin coating.

The adhesive layer 23 has the following features: a) viscosity of 300cps to 900 cps at 25° C.; b) glass transition temperature Tg after acuring of more than 30° C.; c) hardness after a curing of more than “H”;and d) amount of the remaining monomer after a curing of within 10%.

The viscosity of 300 cps to 900 cps at 25° C. is to secure a sufficientthickness of the adhesive layer 23. In other words, when a viscosity ofthe adhesive is smaller than 300 cps, a thickness of the adhesive layer23 is small, and therefore an adhesion strength becomes very weak. Whena viscosity of the adhesive is greater than 900 cps, it is difficult toperform a spin coating.

The glass transition temperature Tg after a curing of more than 30° C.is to prevent the reflecting layer 23 from being transformed during arecording operation to improve recording characteristics of the DVD-R/+Rdisc and to secure a sufficient heat resistance after a recordingoperation. In other words, when the glass transition temperature Tg islower than 30° C., recording characteristics and heat resistance of theDVD-R/+R disc can be lowered.

In the DVD-R/+R disc 200 of FIG. 2, an interface between the dye layer21 and the reflecting layer 22 has a relatively weak adhesion strength.Therefore, when the adhesive layer 23 is greatly contracted during anUV-curing, an interface adhesion between the dye layer 21 and thereflecting layer 23 becomes weak, leading to bad recordingcharacteristics. Also, due to a physical shock or impact, the dye layer21 and the reflecting layer 22 can be separated from each other.Therefore, the adhesive should have a sufficiently low contractioncoefficient not to affect an adhesion between the dye layer 21 and thereflecting layer 22 and preferably have a contraction coefficient ofless than 7.0%.

The hardness after a curing of more than “H” is to improve recordingcharacteristics during a recording operation. When the hardness issmaller than “H”, recording characteristics during a recording operationis lowered.

An amount of the remaining monomer after a curing of within 10% is toimprove a chemical resistance. When an amount of the remaining monomerafter a curing is more than 10%, the dye layer 21 and the reflectinglayer 22 can be damaged, thereby lowering a durability. It is preferablethat a thickness of the adhesive layer 23 is in a range between about 10μm to about 80 μm. If the adhesive layer 23 has a thickness of smallerthan 10 μm, an adhesion strength between the dye layer 21 and thereflecting layer 22 can be lowered. If the adhesive layer 23 has athickness of greater than 80 μm, an interface between the dye layer 21and the reflecting layer 22 can be damaged due to a contraction of theadhesive layer 23 during a curing.

FIG. 3 is a cross-sectional view illustrating an optical recordingmedium according to another preferred embodiment of the presentinvention. A DVD-R/+R disc is described as one example of the opticalrecording medium according to another preferred embodiment of thepresent invention.

The DVD-R/+R disc of FIG. 3 has the same structure as that of FIG. 2except a reflecting layer 34 interposed between an adhesive layer 33 anda dummy substrate 35. In greater detail, the DVD-R/+R disc 300 includesa disc 310 and a dummy substrate 35. The disc 310 includes a dye layer31 and a reflecting layer 32 formed on a substrate 30, and thereflecting layer 34 is formed on the dummy substrate 35. The reflectinglayers 32 and 34 are adhered to each other through an adhesive layer 33.At this point, the reflecting layers 32 and 34 comprise Au, Ag, Cu, Al,or their alloy.

The optical recording medium according to the preferred embodiments ofthe present invention has the following advantages because thepassivation layer is not arranged. Firstly, due to a simplifiedmanufacturing process, a manufacturing yield is improved. Secondly,since a bending of the optical recording medium resulting from aUV-light radiation during a curing of the passivation layer isprevented, recording characteristics can be improved. Thirdly, aproduction cost is low. Fourthly, a high adhesion strength and anexcellent durability can be achieved.

EXAMPLE 1

FIG. 4 is a cross-sectional view an optical recording medium of Example1 according to the preferred embodiments of the present invention.

The optical recording medium of Example 1 is manufactured as follows:first a substrate 40 is provided. The substrate 40 includes pregrooveshaving a track pitch of 0.74 μm, a depth of 150 nm and a width of 350nm. The substrate 40 comprises polycarbonate and has a thickness of 0.6mm.

A cyanine-based organic dye NK-4499 of 0.25 g available from Japanesecompany “Hayashibara” is dissolved in an organic solvent “TFP” of 10 mlto obtain a dye solution. The dye solution is coated on the substrate 40using a spin coating technique to form a dye layer 41. At this point,the spin coating is performed at a speed of 3000 rpm. The dye layer 41is not formed on an outer edge portion of the substrate 40.

The dye layer 41 formed on the substrate 40 is dried at a temperature of80° C. for twenty minutes. Silver (Ag) is deposited on the dye layer 41to a thickness of about 100 nm using a sputtering technique to form areflective layer 42. The reflecting layer 42 is formed to perfectlycover the dye layer 41.

Subsequently, an adhesive is applied on a portion of the reflectinglayer 42. A dummy substrate 45 is laid on the reflecting layer 42 onwhich the adhesive is coated. In this state, a spin coating is performedat a rotation speed of 2000 rpm, whereby an adhesive layer 43 is formed.The adhesive layer 43 is formed to perfectly cover the reflecting layer42.

The adhesive is Desolite 660-006 available from DSM Desotech Inc. ofElgin, Ill., and has a viscosity of 300 cps, a glass transitiontemperature of 32° C., a contraction coefficient of 5.4%, a hardness ofH, and a thickness of about 25 μm.

Thereafter, a UV-light is radiated to cure the adhesive, whereupon thetwo substrates 40 and 45 are firmly adhered, whereby the opticalrecording medium, i.e., DVD-R/+R disc 400 is completed.

As described above, the reflecting layer 42 is formed to cover the dyelayer 41, and the adhesive layer 43 is formed to cover the reflectinglayer 42. In other words, an adhesion enforcing region 47 is formed onboth of an inner peripheral portion and an outer peripheral portion ofthe optical recording medium 400. As a result, an adhesion strengthbetween the substrate 40 and the dummy substrate 45 is increased.

In order to test the DVD-R/+R disc 400 of Example 1, the followingexaminations was performed.

First, a moving picture was recorded on the DVD-R/+R disc 400 of Example1 using a DVD-R recorder (e.g., DVR-200 available from PioneerElectronics). The moving picture recorded on the DVD-R disc 400/+R ofExample 1 was reproduced by a DVD player (e.g., DVD-3030 available fromLG Electronics, DVD-909 available from Samsung Electronics or DV-535Kavailable from Pioneer Electronics). As a result, the recorded movingpicture can be reproduced by all of the DVD players described above.

Also, recording characteristics of the DVD-R/+R disc 400 of Example 1were examined using DDU-1000 available from Pulse Tec. Inc. DVD-R disc400 of Example 1 showed a jitter of 7.8%, a reflectance of 48.0%, and anerror rate of 80, and thus satisfies an international standard.

After the DVD-R/+R disc 400 of Example 1 remained in a circumstance of atemperature of 60° C. and a relative humidity of 80% during six days,the DVD-R/+R disc 400 of Example 1 showed a jitter of 8.0%, areflectance of 48.5%, and an error rate of 90. That is, the DVD-R/+Rdisc 400 of Example 1 showed an excellent heat resistance and anexcellent humidity resistance.

Further, ten DVD-R/+R discs of Example 1 were dropped from a height of1.5 m and then examined. All of ten DVD-R/+R discs were not broken andthus showed an excellent impact resistance.

EXAMPLE 2

An optical recording medium of Example 2 is manufactured identically toExample 1 except the following: the adhesive layer 43 is made of MK-1010made by the inventor of the present invention wherein MK-1010 has aviscosity of 650 cps, a glass transition temperature of 125° C., acontraction coefficient of 6.3%, and a hardness of H. Also, the adhesivelayer has a thickness of 40 μm, and the reflecting layer is made of anAg—Cu—Au alloy.

The optical recording medium of Example 2 showed recordingcharacteristics of a jitter of 7.8%, a reflectance of 48.5%, and anerror rate of 50.

After the optical recording medium of Example 2 remained in acircumstance of a temperature of 60° C. and a relative humidity of 80%during six days, the optical recording medium of Example 2 showed ajitter of 7.8%, a reflectance of 49.0%, and an error rate of 60. Thatis, the optical recording medium of Example 2 showed an excellent heatresistance and an excellent humidity resistance.

Further, ten optical recording mediums of Example 2 were dropped from aheight of 1.5 m and then examined. All of ten optical recording mediumof Example 2 were not broken and thus showed an excellent impactresistance.

COMPARISON EXAMPLE 1

An optical recording medium of Comparison example 1 is manufacturedidentically to Example 1 except an addition of a passivation layer. Thepassivation layer is formed between the reflecting layer 42 and thedummy substrate 45 such that SK-3200 available from Sony ChemicalCorporation is coated on the reflecting layer 42 and then cured by aUV-light.

The optical recording medium of Comparison example 1 showed recordingcharacteristics of a jitter of 8%, a reflectance of 48.5%, and an errorrate of 100.

After the optical recording medium of Comparison example 1 remained in acircumstance of a temperature of 60° C. and a relative humidity of 80%during six days, the optical recording medium of Comparison example 1showed a jitter of 8.5%, a reflectance of 49.0%, and an error rate of150. That is, the optical recording medium of Comparison example 1showed a heat resistance and a humidity resistance inferior to Example 2having no passivation layer.

Further, ten optical recording mediums of Comparison example 1 weredropped from a height of 1.5 m and then examined. All of ten opticalrecording mediums of Comparison example 1 were not broken and showed anexcellent impact resistance.

COMPARISON EXAMPLE 2

An optical recording medium of Comparison example 2 is manufacturedidentically to Example 2 except the adhesive layer and the passivationlayer. The adhesive layer is formed using SK-6000 available from SonyChemical Corporation having a viscosity of 300 cps, a glass transitiontemperature of 89° C., a contraction coefficient 8.3%, and a hardness ofH. The passivation is formed between the reflecting layer 42 and thedummy substrate 45 such that SK-3200 is coated on the reflecting layerand then cured by a UV-light.

The optical recording medium of Comparison example 2 showed recordingcharacteristics of a jitter of 8.4%, a reflectance of 48.5%, and anerror rate of 120. That is, recording characteristics are lowered.

After the optical recording medium of Comparison example 2 remained in acircumstance of a temperature of 60° C. and a relative humidity of 80%during six days, the optical recording medium of Comparison example 2showed a jitter of 10.0%, a reflectance of 53.0%, and an error rate of500. That is, the optical recording medium of Comparison example 2showed a heat resistance and a humidity resistance inferior to Example 2having no passivation layer.

Further, ten optical recording mediums of Comparison example 2 weredropped from a height of 1.5 m and then examined. Among ten opticalrecording mediums of Comparison example 2, the two were broken. Thisindirectly shows that an adhesion strength between the dye layer 41 andthe reflecting layer 42 is significantly lowered due to a greatcontraction generated during a UV-light curing.

COMPARISON EXAMPLE 3

FIG. 5 is a cross-sectional view illustrating an optical recordingmedium of Comparison example 3. The optical recording medium 500 ismanufactured identically to Example 2 except that an adhesion enforcingregion 57 is formed only on an outer peripheral region of the opticalrecording medium 500.

The optical recording medium of Comparison example 3 showed recordingcharacteristics of a jitter of 7.5%, a reflectance of 48.5%, and anerror rate of 50.

After the optical recording medium of Comparison example 3 remained in acircumstance of a temperature of 60° C. and a relative humidity of 80%during six days, the optical recording medium of Comparison example 3showed a jitter of 10.8%, a reflectance of 52.0%, and an error rate of600. That is, the optical recording medium of Comparison example 3showed a heat resistance and a humidity resistance inferior to Example2.

Further, ten optical recording mediums of Comparison example 3 weredropped from a height of 1.5 m and then examined. Among ten opticalrecording mediums of Comparison example 3, the four were broken. Thisindirectly shows that the adhesion enforcing region 57 should be formedon both an inner peripheral portion and an outer peripheral portion ofthe optical recording medium.

COMPARISON EXAMPLE 4

An optical recording medium of Comparison example 4 is manufacturedidentically to Example 2 except that the adhesive layer is made ofDesolite 650-002 having a viscosity of 10 cps, a glass transitiontemperature of 26° C. and a contraction coefficient of 7.0%, and has athickness of 8 μm.

The optical recording medium of Comparison example 4 showed recordingcharacteristics of a jitter of 8.8%, a reflectance of 48.5% and an errorrate of 200. That is, recording characteristics of the optical recordingmedium of Comparison example 4 is lower than Example 2. When ten discswere dropped from a height of 1.5 m, seven discs were broken. That is,since a thickness of the adhesive layer is relatively thin, i.e., lowerthan 10 μm, an adhesion strength of the adhesive layer is lowered.

As described hereinbefore, since the passivation layer is not arranged,a manufacturing process is simplified, and also excellent recordingcharacteristics, excellent heat resistance and excellent moistureresistance can be achieved. Further, due to an adhesion enforcing regionformed on both an inner peripheral region and an outer peripheral regionof the disc, an adhesion strength between the two substrates isimproved, leading to a high durability.

While the invention has been particularly shown and described withreference to preferred embodiments thereof, it will be understood bythose skilled in the art that the foregoing and other changes in formand details may be made therein without departing from the spirit andscope of the invention.

1. An optical recording medium, comprising: a disc including a dye layerand a reflecting layer formed on a substrate; a dummy substrate; and anadhesive layer adhering the disc and the dummy substrate.
 2. The mediumof claim 1, wherein an adhesive of the adhesive layer is cured byUV-light.
 3. The medium of claim 1, wherein the adhesive layer has aviscosity of 300 cps to 900 cps at 25° C., a glass transitiontemperature Tg after a curing of more than 30° C., a hardness after acuring of more than “H”, and an amount of the remaining monomer after acuring of within 10%.
 4. The medium of claim 1, wherein the reflectinglayer covers exposed portions of the dye layer, and the adhesive layercovers exposed portions of the reflecting layer.
 5. The medium of claim1, wherein adhesion enforcing regions are arranged on both an innerperipheral region and an outer peripheral region of the opticalrecording medium.
 6. The medium of claim 1, further comprising, areflecting layer formed on the dummy substrate.
 7. The medium of claim1, wherein the reflecting layer comprises Ag, Au, Al, Cu, or theiralloy.
 8. The medium of claim 1, wherein the dye layer comprises acyanine-based dye, a hemicyanine-based dye, an azo-based dye, atriphenylmetane-based dye, or a combination of two or more thereof. 9.The medium of claim 1, wherein the adhesive layer has a thickness of 10μm to 80 μm.